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Naughty?Well, OK, we can't exactly call these stocks naughty. But none of them get much love from our 73,000-person-strong Motley Fool CAPS community of amateur and professional stock pickers.

To the contrary -- when it comes to these stocks, CAPS investors have gone thumbs down more often than film critic Roger Ebert. They don't believe any of these stocks are worth owning, and that some may be worth shorting.

Which of today's candidates is worst? Read on, dear Fool.

WorseWe begin with plastic decking maker Trex, which yesterday cut its 2007 sales guidance to $315 million to $335 million from $330 million to $350 million. A $17 million reserve for defective products is partially to blame.

Not that Fools were surprised. Here's how bearish CAPS investor willowman put it June: "Plastic lumber looks crappy and is too expensive, I wish I would have shorted this stock 2 years ago, but it will go down more."

Trex is down nearly 60% since.

WorserNext up is dental laser maker BIOLASE, which took a beating after announcing sharp declines in revenue and earnings in Q3. Management -- or I should say "new" management, for director Federico Pignatelli replaced CEO Jeffrey Jones -- blamed the shortfall on a lack of interest in its Waterlase technology. Quoting Pignatelli from the press release:

Revenue results for the quarter ended September 30, 2007 were well below our expectations, notwithstanding the typically slower summer quarter. Sales of our diode laser systems continued to outpace those in the same quarter of 2006, but sales of WaterlaseMD all-tissue laser systems showed a significant decrease. [Emphasis added.]

Therein lies the problem. Even if you believe BIOLASE when it calls Waterlase a clinically superior technology, or have confidence in its distribution deal with Henry Schein (NASDAQ:HSIC), there weren't enough buyers of the product in Q3.

And for the record: Waterlase accounted for 74% of revenue in Q1. No wonder Jones was shown the door.

WorstBut our winner is US Airways, which on Tuesday reported miserable traffic numbers for October. Revenue passenger miles declined 1.5% and capacity fell 5.5%. Load factor, meanwhile, rose to 80.5%, a new record. (Here's a decoder ring for those confused by the jargon.)

In other words: US Airways flew less. But the times it did fly, its aircraft were packed tighter than sardines in a can.

Yet none of this is why the airline tops today's list of losers. This is: US Airways ranked worst among the major airlines in terms of customer complaints in September, according to Department of Transportation statistics.

Fewer flights. Packed aircraft. Subpar service. And this was the company that once promised to rescue Delta (NYSE:DAL) via a merger? Puh-leeze. US Airways -- Tuesday's worst stock in the CAPS world.

Do you agree? Disagree? Let us know what you think by signing up for CAPS today. It's 100% free to participate.

See you back here tomorrow for more stock horror stories.

Fool contributor Tim Beyers, who is ranked 12,344 out of more than 73,000 participants in CAPS, hopes that Keith Olbermann doesn't mind the blatant theft of his "Worst Person in the World" segment from Countdown. Remember, Keith, imitation is the sincerest form of flattery.

Tim didn't own shares in any of the companies mentioned in this article at the time of publication. Find Tim's portfolio here and his latest blog commentary here. The Motley Fool's disclosure policy thinks that cooked spinach is the worst veggie in the world.

Author

Tim Beyers first began writing for the Fool in 2003. Today, he's an analyst for Motley Fool Rule Breakers and Motley Fool Supernova. At Fool.com, he covers disruptive ideas in technology and entertainment. Find him online at timbeyers.me or send email to tbeyers@foolcontractors.com. For more insights, follow Tim on Twitter.